1. Field of the Invention
The invention relates to implantable devices or endoluminal prostheses, such as stents. More particularly, this invention relates to a coating for a stent and methods for making the same.
2. Description of the Background
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. A catheter assembly having a balloon portion is introduced percutaneously into the cardiovascular system of a patient via the brachial or femoral artery. The catheter assembly is advanced through the coronary vasculature until the balloon portion is positioned across the occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially press against the atherosclerotic plaque of the lesion for remodeling of the vessel wall. The balloon is then deflated to a smaller profile to allow the catheter to be withdrawn from the patient""s vasculature.
A problem associated with the above procedure includes formation of intimal flaps or torn arterial linings, which can collapse and occlude the conduit after the balloon is deflated. Vasospasms and recoil of the vessel wall also threaten vessel closure. Moreover, thrombosis and restenosis of the artery may develop over several months after the procedure, which may necessitate another angioplasty procedure or a surgical by-pass operation. To reduce the partial or total occlusion of the artery by the collapse of arterial lining and to reduce the chance of the development of thrombosis and restenosis, an expandable, intraluminal prosthesis, one example of which is a stent, is implanted in the lumen to maintain the vascular patency.
Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically stents are capable of being compressed, so that they can be inserted through small cavities via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in the patent literature disclosing stents that have been applied in PTCA procedures include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor. Mechanical intervention via stents has reduced the rate of restenosis as compared to balloon angioplasty. Yet, restenosis is still a significant clinical problem with rates ranging from 20-40%. When restenosis does occur in the stented segment, its treatment can be challenging, as clinical options are more limited as compared to lesions that were treated solely with a balloon.
Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. In order to provide an efficacious concentration to the treated site, systemic administration of such medication often produces adverse or even toxic side effects for the patient. Local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery thus produces fewer side effects and achieves more favorable results. This invention provides for a stent coating capable of sustained local delivery of therapeutic substances and methods of forming the coating.
A method of coating a stent is provided. The method includes forming a first layer supported by a stent substrate and patterning the first layer by removing portions of the first layer.
In some embodiments, the method additionally includes forming a primer layer on the surface of the stent substrate prior to forming the first layer.
In other embodiments, the method includes forming a second layer on the remaining portions of the first layer. The first layer may contain a first substance and the second layer may contain a second substance different than the first substance. The first and second substances may be active ingredients, radiopaque elements, or radioactive isotopes.
In other embodiments, the act of patterning the first layer includes forming a second layer on the surface of the stent prior to forming the first layer. The second layer is patterned to form vias in the second layer. Such patterning may be performed by applying a laser discharge to selected areas of the second layer. The first layer is formed on the remaining portions of the second layer and in the vias. The second layer is patterned to remove portions of the first layer disposed on the remaining portion of the second layer to pattern the first layer.
In still other embodiments, the act of patterning the first layer includes forming a second layer on the surface of the stent prior to forming the first layer and patterning the second layer to expose portions of the surface of the stent. The act of patterning the first layer also includes forming depots in the stent between the remaining portions of the second layer, wherein the first layer fills the depots, and removing the remaining portions of the second layer to remove portions of the first layer disposed on the remaining portions of the second layer, wherein the first layer remains in the depots. A third layer may be formed on the surface of the stent and over the first layer in the depots.
In still other embodiments, the act of patterning the first layer includes forming a second layer on the first layer and patterning the second layer to form vias in the second layer to expose portions of the first layer. The act of patterning the first layer also includes removing the exposed portions of the first layer, wherein portions of the first layer positioned underneath the remaining portions of the second layer remain essentially undisturbed, and removing the remaining portions of the second layer to form a patterned first layer. A third layer may be formed on the remaining portions of the first layer.
A coated stent produced in accordance with the various methods is also provided. The coated stent includes a first layer and a discontinuous second layer separated by the first layer. The first layer is a discontinuous layer separated by the second layer so as to create an alternating pattern of the first and second layers on the surface of the stent. In accordance with another embodiment, the discontinuous first and second layers can be disposed on a primer layer.